Storage tanks are used to hold a variety of liquids. Because the tanks are totally closed, conditions inside the tank, such as the liquid level is not readily apparent or easily ascertained. The liquid level may be measured by inserting a dip stick into the tank.
Gauges are often inserted into tanks holding various materials to measure various conditions within the tank such as the volume of liquid remaining in the tank. Problems arise because the liquid contained within the tank can adversely affect the gauge in a number of ways. Material such as crude oil or salt water can clog, or freeze the gauge or cause the gauge to deteriorate resulting in the gauge producing inaccurate readings.
In an attempt to solve the problems associated with gauge deterioration and clogging, devices which isolate the gauge from the liquid were designed which place a second liquid between the liquid in the tank and the gauge. Such devices include a surface or bladder on which the liquid acts. The surface contains the second liquid within an enclosed space. The surface then transmits the pressure to the second liquid which in turn acts on the gauge.
These isolating devices prevent the fouling and corrosion of the gauge. However, such gauge isolating devices require attachment to the inside of the tank thereby requiring full drainage of the tank and requiring personnel to enter the tank. Furthermore, the conditions inside the tank can be inhospitable to a person attempting to enter for measuring purposes. Moreover, additional problems have been encountered in the operation and installation of the isolating device when operating a gauge with an isolation device in cold climates, since the liquid within the device tends to freeze.